"We had the most pro-choice candidate in decades, but we don't have the most pro-choice president," said Terry O'Neill, president of the half-million-strong National Organisation of Women.

"The Stupak-Pitts amendment is a giant leap in the direction of making abortion completely inaccessible to all of us," O'Neill said.

Sixty-four Democrats joined 176 Republicans to vote for the amendment, named after co-authors Representative Bart Stupak, a Democrat, and Republican lawmaker Joseph Pitts.

"They said they wouldn't have been able to get health care reform passed without this amendment," said O'Neill.

"And they say, 'What are you worried about? At least we got health care reforms through'.

"We want the Senate to drop the amendment, and if they don't, we are going to pressure the president not to sign it. They should be more concerned that they have passed a bill that gives women only partial health care than about angering the Catholic church," O'Neill said.

Stupak-Pitts was drafted by men, passed by a House of Representatives with only 16 per cent of women lawmakers and backed by the all-male US Conference of Catholic Bishops (USCCB), O'Neill noted.

"Here come all these men, who have never had to worry about missing a period, and they pass a health care bill for 49 per cent of the population," she said.

"Well, as one of the 51 per cent who only got a partial health care bill, let me say we are irritated," she said, adding that she was still waiting "for Obama the president to deliver on the promises made by Obama, the candidate".

Liza Sabater, a former professor at Rutgers University turned full-time blogger, accused Democratic House lawmakers of "throwing women under the bus" by voting for the amendment.

She listed on her website the names of Democrats who voted in favour of the amendment.

The amendment would bar the proposed federal government insurance programme, known as the "public option", from paying for abortion, except to save the life of the mother or in cases of rape or incest.

It would also block the use of proposed federal subsidies - tax breaks for people and small businesses with low incomes or revenues to help pay for health insurance - to fund abortions.

"If anyone on your private plan, which you are paying for out of your own pocket, is subsidised, that plan has to exclude abortion coverage" under the amendment, O'Neill told AFP.

The amendment does provide one way for women to have an abortion - by purchasing a "single-service rider" to cover the voluntary termination of pregnancy.

But Cecile Richards, president of the Planned Parenthood Federation of America - the biggest provider of abortions in the United States - decried abortion riders as "discriminatory and illogical".

"Women do not plan to have unintended pregnancies or medically complicated pregnancies that require ending the pregnancy," she said.

"Proposing a separate 'abortion rider' or 'single-service plan' is tantamount to banning abortion coverage ... no insurance company would offer such a policy."

The USCCB said the amendment "honoured President Obama's commitment to the Congress and the nation that health care reform would not become a vehicle for expanding abortion funding."

Pro-life groups vowed to make sure it did not get gutted from the proposed legislation on health care when it goes before the Senate.

"We will remain vigilant in watching the final language of the Senate bill to ensure that pro-life protections remain in the final health care reform bill," said Charmaine Yoest, the president and chief executive of Americans United for Life Action.

O'Neill warned that, should that happen, "the United States will take a huge step backward toward the back alley".